The present invention relates to a ribbon lift-up apparatus of an electronic typewriter having printing and correction ribbons.
The conventional ribbon lift-up apparatus employed in the electronic typewriter having printing and correction ribbons is shown in FIG. 7. With key operation for printing, a printing ribbon lift-up signal actuates a ribbon motor 1 to rotate 90 degrees in the forward direction A, rotating a disc cam 2 by 90 degrees in the direction A'. The ribbon motor 1 has a pinion gear 1' which intermeshes with the edge 2' of the disc cam 2 whereby the disc cam 2 may be rotated by rotation of the ribbon motor 1. The pin 4 of a cam follower 3 is thus guided into a printing cam groove 5 having a smaller radius. Then, a ribbon cartridge holder 6 linked with the cam follower 3 rotates around the axis 7, whereby a printing ribbon cartridge 8 loaded on the cartridge holder 6 is lifted up to the hammer (not shown) position for printing. In the intermittent printing operation, the ribbon motor 1 that has rotated 90 degrees in the forward direction A rotates 90 degrees in the direction B, lowering the printing ribbon cartridge 8 before the next lift-up operation for printing. In the continuous printing operation, the ribbon motor 1 that has rotated 90 degrees in the direction A further rotates 90 degrees in the forward direction A for the second type printing. Namely, the second type is printed when the disc cam 2 rotates 180 degrees in the forward direction A from the home position. The disc cam 2 rotates alternately in the forward and reverse directions A', B' between the rotation angles of 90 and 180 degrees from the home position, in continuous printing.
With key operation for correction, on the other hand, a correction ribbon lift-up signal actuates the ribbon motor 1 to rotate 180 degrees in the reverse direction B, thus rotating the disc cam 2 150 degrees in the reverse direction B'. Accordingly, the cam follower pin 4 is guided into a correction cam groove 9 having a larger radius. Then, the ribbon cartridge holder 6 rotates around the axis 7 by a larger degree so that the correction ribbon 10 mounted on the cartridge holder 6 is lifted up to the specified position for correction. The correction ribbon 10 is lowered as the ribbon motor 1 rotates in the direction A, rotating the disc cam 2 in the direction A'.
A specified length (not shown) of the printing or correction ribbon is wound every time before the above-mentioned ribbon lift-up operation. In the conventional ribbon lift-up apparatus in which the disc cam 2 rotates in the forward and reverse directions alternately for each type printing, the printing ribbon needs to be wound for both forward and reverse rotation of the disc cam 2. Consequently, the printing ribbon is wound in the correction operation when the disc cam 2 rotates reversely, which is quite inconvenient from an economical standpoint. In addition, the alternate forward and reverse rotations of the disc cam 2 hampers fast continuous printing operation.